The invention relates mainly to an actuator designed to be placed permanently down an oil or gas production well for the purpose of controlling at will the displacement of a moving part therein.
Such an actuator can be used, in particular, for controlling an on/off valve, a variable flow rate valve, or any other device required to remain at the bottom of a well for a prolonged period, e.g. about 5 years, without being subjected to maintenance.
The invention also relates to a flow rate adjuster device fitted with such an actuator.
Whatever their functions, actuators used at present in downhole installations are generally fitted with dynamic sealing gaskets interposed between the moving portions and the fixed portions of the actuators.
In particular, dynamic sealing gaskets are used both in hydraulic actuators of the piston-and-cylinder type, and in electromechanical actuators of the type incorporating an electric motor and a screw-and-nut system.
When frequent maintenance is possible, elastomer gaskets are used which provide excellent sealing, but which need to be replaced very often.
When it is desired to space out maintenance operations, it is the practice to replace elastomer gaskets with gaskets of other shapes and kinds, such as metal or thermoplastic gaskets. Nevertheless, although the lifetime of such gaskets is greater than that of elastomer gaskets, they still need to be replaced quite often, specifically because of the particularly severe temperature (150xc2x0 C. to 175xc2x0 C.) and pressure (1000 bars to 1500 bars) conditions that obtain downhole, because of the corrosive nature of well fluid, and because of the sand and gravel that are often present.
Whatever the kind of gasket used, it is essential to guarantee perfect sealing of the actuator throughout the period that extends between two consecutive maintenance operations. The slightest drop of well fluid penetrating into the actuator could make it inoperative, e.g. by giving rise to a short circuit.
In order to balance the very large pressure present downhole, most actuators operating in that environment contain a hydraulic fluid. A compensation device is then associated with the actuator for the purposes of taking account of variations in pressure and temperature and of continuously balancing the pressures between the well fluid and the hydraulic fluid contained in the actuator. In general, the compensation device is also fitted with dynamic gaskets which give rise to problems analogous to those of the gaskets fitted to the actuator proper.
A particular object of the invention is to provide an actuator designed to stay downhole without maintenance for a period of time that is much longer than with presently-existing actuators, e.g. about 5 years.
According to the invention, there is provided a downhole actuator comprising control means suitable for displacing a moving member relative to a fixed casing along a longitudinal direction of a well, at least one zone of the casing containing a fluid at substantially the same pressure as the bottom of the well, the actuator further comprising at least one sealing bellows interposed along said direction between the casing and the moving member, the sealing bellows defining at least a portion of said zone.
The use of at least one bellows for sealing the actuator makes it possible either to omit the dynamic sealing gaskets normally used for this purpose, or else to protect them from the downhole atmosphere if they cannot be omitted. Under such circumstances, the gaskets no longer come directly into contact with the fluid present downhole.
Preferably, the actuator comprises a compensation bellows connected to said zone and including a radial wall subjected to the downhole pressure.
The use of a bellows to compensate pressure and temperature variations in the well makes it possible to perform this function while dispensing with all of the dynamic sealing gaskets used in existing compensation devices.
In a first embodiment of the invention, the sealing bellows and the compensation bellows are mounted end-to-end on the same axis. One end of the compensation bellows is then fixed to the casing, and the sealing bellows connects the moving member to the rim of a central opening formed in said radial wall of the compensation bellows.
In a second embodiment of the invention, the sealing bellows and the compensation bellows are separate. The sealing bellows then connects the moving member to the casing and the compensation bellows communicates separately with the above-specified zone of the casing.
In this case, various arrangements are possible depending on the location of the moving member relative to the fixed casing.
Thus, the moving member can be placed beyond one end of the fixed casing. A single sealing bellows then connects the moving member to said end of the casing.
In this case, an end of the compensation bellows remote from the radial wall is fixed either to one end of the casing or else to a portion of the moving member situated outside the casing. In which case, a passage is formed in the casing or in the moving member to connect the above-specified zone to the compensation bellows.
The moving member can also be placed facing an opening formed in the fixed casing. Two sealing bellows then connect the moving member to the casing on respective opposite sides of the opening. In this case, the volume of the zone filled with hydraulic fluid remains substantially constant.
In this case, an end of the compensation bellows remote from the radial wall is fixed to one end of the casing and communicates with said zone.
Advantageously, the sealing bellows and the compensation bellows are made of stainless steel.
In particular, the actuator can be of the electromechanical type. In which case, the control means comprises an electric motor housed in the casing and an intermediate member is rotatably mounted in the casing and suitable for being rotated by the electric motor. The intermediate member then engages the moving member via a screw-and-nut type link.
In general, the casing can either be fixed on the outside of the length of production tubing, parallel thereto, or else it surrounds said length coaxially.
The actuator can also be of the hydraulic type. The control means then comprise a hydraulic piston and cylinder actuated by a pressure source. In which case, the moving member is secured to the piston and is suitable for sliding in sealed manner in the casing which defines at least one control chamber connected to the pressure source. The above-specified zone is then formed outside said chamber, and is separated therefrom by at least one sealing gasket, and is connected to a supply of fluid that is defined at least in part by the compensation bellows.
The invention also provides a downhole flow rate adjuster device including an actuator, a length of production tubing in which at least one opening is formed, and a jacket slidably mounted relative to said length, the actuator having control means suitable for displacing a moving member linked to said jacket relative to a fixed casing linked to said length in a longitudinal direction of the well, at least one zone of the actuator containing a fluid that is at substantially the same pressure as the bottom of the well, said device further comprising at least one sealing bellows interposed in said direction between the casing and the moving member, the sealing bellows defining at least a portion of said zone.